People who owe Plano and Grand Prairie civil fines for running red lights will soon have their vehicle registrations blocked by the state. But the effectiveness of that tactic in recovering millions in unpaid fines — or getting motorists to drive more safely — remains to be seen.

Neither city has a contract with its county tax assessor-collector to help enforce the block. So while drivers with outstanding civil violations in those cities will get rebuffed by the Texas Department of Motor Vehicles, they could walk into their county tax office and still receive a registration renewal.

Plano police spokesman David Tilley said his department recognizes that loophole could undermine the program’s goal.

“We’re hopeful it won’t,” he said.

The program only involves people who receive civil violations for being caught by a red light camera. It doesn’t include people who receive a ticket for a moving violation from an officer.

Fort Worth also doesn’t have a contract with its county tax assessor-collector, though one is in the works. Unexpectedly, when that city first teamed with the state to block vehicle registration renewals, fewer people paid their red light camera violations.

Garland does have a contract with its county tax assessor-collector and the DMV. Garland police spokesman Joe Harn didn’t have data immediately available Tuesday. But he said the number of people paying for running red lights rose after the blocks began.

Harn attributes almost half of this year’s paid fines to the registration blocks.

“When we were able to work that out with the county, then it has picked up our fines,” Harn said.

But Plano, which falls almost wholly within Collin County, may not have Garland’s luck. County Tax Assessor-Collector Kenneth Maun previously declined to block registration renewals for people who don’t pay for driving on toll roads. Tilley said his department isn’t expecting Maun to strike a deal on red light camera violators, either.

“Last I heard, he’s not flagging them,” Tilley said.

Maun didn’t return a phone call seeking comment Tuesday.

Grand Prairie straddles the Dallas-Tarrant county line. A police spokesman did not return phone calls seeking comment Tuesday. But tax assessor-collectors for both counties said they’d entertain entering into an agreement to enforce the DMV block at tax office locations.

Dallas County Tax Assessor-Collector John Ames already has agreements in place with Balch Springs and Garland but not University Park.

Tarrant County Tax Assessor-Collector Ron Wright said he plans to work out agreements with Fort Worth, Arlington, Bedford, Haltom City, Hurst, North Richland Hills and Richland Hills.

Denton County Tax Assessor-Collector Michelle French has agreements in place with Denton and Roanoke.

Red light cameras have been a controversial public safety tool since they were introduced in Texas a decade ago. Garland was the first to take advantage of a state law allowing cities to charge civil penalties for people caught running red lights on camera.

Motorists — and even lawmakers — accused cities of using the cameras solely for revenue generation. But police officials swear by them as ways to make their cities safer.

Half of red light fines go to the state. Tilley said the half the cities keep must be used on traffic-related expenses. Plano spends its red light camera revenue on backup generators for traffic lights, sand trucks and overtime for officers enforcing laws against driving while intoxicated.

“Every bit of the money we get has to go into a traffic safety fund,” Tilley said.

Harn and Tilley both said accidents at intersections where cameras were installed fell dramatically. The first year Plano used the cameras, the number of crashes involving red light runners fell 32.4 percent at intersections where they were installed.

“From that standpoint it has been an effective tool,” Harn said.

Both men said the overall goal of the fines — and enforcement — is to deter motorists from driving dangerously.

“People die as a result of running red lights,” Tilley said.

Follow Brandon Formby on Twitter at @brandonformby.

AT A GLANCE: Going for the block

More than 65 Texas cities contract with the state’s Department of Motor Vehicles to block vehicle registration renewals for people who owe civil fines for running red lights. But without a contract with a county tax assessor-collector, that city’s violators can still get registration renewals. Here’s a look at area cities with DMV contracts and whether they also have county contracts.

Arlington: Expected

Balch Springs: Yes

Bedford: Expected

Denton: Yes

Fort Worth: Expected

Garland: Yes

Grand Prairie*: No

Haltom City: Expected

Hurst: Expected

North Richland Hills: Expected

Plano: No

Richland Hills: Expected

Roanoke: Yes

University Park: No

*DMV contract currently being finalized

SOURCES: Texas Department of Motor Vehicles, DMN research

RED LIGHT AMNESTY PERIOD

Grand Prairie and Plano are giving people with unpaid red light camera violations until Dec. 1 before they begin working with the Texas Department of Motor Vehicles to block vehicle registration renewals.